1. Field of the Invention
The present invention relates to the art of food preservation and pertains specifically to a method which uses gelled polyuronic acids to more successfully preserve the natural texture of diced, fresh fruit and vegetable products.
2. Description of the Prior Art
In a widely used procedure for canning diced tomatoes and other diced fruits and vegetables, an initial treatment step with steam or caustic facilitates removal of the food product's outer skin. Thereafter, the food product is diced to the desired size and is blended with appropriate additives for firming the dices and preventing spoilage. A soluble source of calcium, e.g., calcium chloride, is a well-known additive for enhancing texture in such materials. Calcium ions absorbed into the dices reinforce the inter-cellular structure, presumably by forming crosslinks with natural pectin in the material. Citric acid is added as a pH control to enhance flavoring and more importantly to retard spoilage. Generally, the food product is then heat treated, either before or after the canning operation, to inactivate molds and yeasts.
Unfortunately, heat and acid sterilization treatments typically cause a marked deterioration in the shape, particle size and texture of canned fruit or vegetable products, even after thorough treatment with a soluble calcium source, e.g., calcium chloride. For this reason, development of an improved canning procedure which provides better retention of the food product's original texture would represent an important advance in the canning art. It has now been discovered that by incorporating a gelled polyuronic acid, e.g., calcium alginate, in the diced, fresh fruit or vegetable product an improvement in texture is obtained.
Calcium alginate has been used previously to encapsulate macerated fruits and berries. In this prior procedure, a soluble calcium source, e.g., aqueous calcium chloride solution, is initially blended with macerated material and a drop of the mixture is thereafter contacted with alginate solution, eg. an aqueous solution of sodium alginate. After suitable contacting, a gel forms around the drop, and quickly thickens until it becomes virtually impenetrable by surrounding alginate solution. If desired, excess alginate solution retained on the drop can be gelled by treatment with additional calcium salt solution. A similar procedure has also been used to encapsulate flavoring agents for ice cream, custard, jelly and the like. A primary disadvantage of this procedure is that the natural texture of the original food product is destroyed by maceration. It should also be noted that this procedure is designed merely to encase pureed material in a shell of gelled alginate.
In another prior art procedure, a calcium alginate gel is formed within and around dehydrated food products by initially impregnating the partially dehydrated food product with calcium salt solution, followed by further vacuum dehydration and then rapid impregnation with alginate solution. The initial dehydration step tends to rupture the cellular structure of the material, creating numerous channels and capillaries into its interior. Generally, on rehydration damage done to the food's cellular structure becomes evident as a total loss in the materials natural texture. This prior art process attempts to avoid this problem on reconstitution apparently by forming a secondary structure or skeleton of a gelled hydrocolloid throughout the inner-channeled matrix produced by the initial dehydration. As disclosed, this process may be used prior to canning the food product, and it is claimed that such treatment enables the food product to retain its initial shape and appearance after freezing and thawing or after cooking. Unfortunately, the dehydration step not only alters the natural texture of the fresh food product but also removes various juices and flavoring constituents from the product generally making it less palatable. Moreover, even though the coating penetrates the exterior surface of the material through the artificially created channels, this technique merely coats the food substrate with a gel as in the prior procedure.
It is an object of the present invention to provide a method for treating diced, fresh fruit and vegetable products that preserves their natural texture even through the rigors of conventional canning procedures.
It is another object of this invention to provide a method for treating diced, fresh fruit and vegetable products so that their natural texture is not significantly altered by conventional heat and acid sterilization procedures.